Core-shell type composites based on polyimide-derived carbon nanofibers and manganese dioxide for self-standing and binder-free supercapacitor electrode applications

Abstract

We herein report the microstructure and electrochemical performance of core-shell type composites based on polyimide (PI)-derived carbon nanofiber (CNF) coated with manganese dioxide (MnO2) for potential applications as self-standing and binder-free supercapacitor electrode materials. For the purpose, a series of core-shell type CNF/MnO2 composites was fabricated via electrospinning of PI precursor with poly(vinyl pyrrolidone) (PVP), imidization of as-spun nanofibers, carbonization of PI/PVP nanofibers into neat CNFs, and coating of neat CNFs with MnO2 at different dipping time of 0–60 min. The Raman, X-ray diffraction and electron microscopic analyses of the core-shell type CNF/MnO2 composites revealed that MnO2 nanowhiskers were coated well on the CNFs with a turbostratic graphitic structure and their coating thickness increased with the dipping time. The electrical conductivity was measured to decrease slightly from 3.6 S/cm for the neat CNF to 1.6 S/cm for CNF/MnO2 composites with increasing the thickness of MnO2 coating layer. As a result of synergistic effects, the core-shell type CNF/MnO2 composite, fabricated at the dip-coating time of 10 min, exhibited a maximum electrochemical performance such as specific capacitance of ~456 F/g at 10 mV/s, energy density of ~17.8 Wh/kg, and power density of ~320 W/kg, in addition to good operational stability of ~95.8% capacitance retention after charge-discharge tests of 3000 cycles.